Structural Study of a Benzidine-Vermiculite Intercalate Having a High Tetrahedral-Iron Content by ⁵⁷Fe Mössbauer Spectroscopy

Abstract

Abstract-57Fe Mrssbauer spectra obtained at room temperature and 78 K for natural Mg-saturated, Casaturated, and benzidinium-intercalated vermiculite having a high tetrahedral iron content are presented. For all samples the spectra were computer-fitted with five overlapping doublets, representing Fe in both tetrahedral and octahedral sites. One doublet has parameters consistent with the weathered ilmenite known to be present as inclusions. For the intercalated vermiculite, the 6 value of the doublet assigned to the tetrahedral Fe 3+ increased with respect to the untreated sample, suggesting that the electron densities about the Fe sites had decreased following intercalation. A charge movement from the silicate layers towards the interlayer monovalent benzidinium ions is also implied. The direction of this charge movement is opposite to that found when blue monopositive radical cations form on montmorillonite surfaces. The M6ssbauer evidence suggests the absence of an interlayer-Fe 3 § complex.

Detection of Tetrahedral Fe3+ Sites in Nontronite and Vermiculite by Mössbauer Spectroscopy

“…This vermiculite contains about 70% of its Fe in tetrahedral coordination as indicated by chemical analysis and Mtssbauer spectroscopy (Cardile and Slade 1987). Cardile and Slade (1987) satisfactorily fit the MSssbauer spectrum of this vermiculite using a model that included: one IVFe3+ doublet; one trans VIFe3+ doublet; one cis VIFe3+ doublet; and one doublet having IS = 0.6 mm/s and QS = 1.65 ram/s, attributed to ilmenite growths. A similar model was used in the present work (Table 3), and the two sets of Mtssbauer parameters are in good agreement for the 2-layer hydrate.…”

“…One way to test this is to demonstrate a similar effect to that observed in the M6ssbauer spectrum of SWa-1 by Luca and Cardile (1989) on samples which indisputably contain IVFe3 § The Koegas nontronite examined by Goodman et al (1976) and the Phalaborwa vermiculite examined by Cardile and Slade (1987) are good candidates because they have been shown by chemical analysis to contain about 16% Fe 3+ substitution in the tetrahedral sheet. This IVFe3 § content was corroborated by M6ss-bauer spectroscopy.…”

“…Bingham nontronite was obtained in the Ca-exchanged form from C. M. Cardile, and has been described in greater detail by Cardile (1985) and Cardile et al (1986). The Phalaborwa vermiculite was the same sample used in Cardile and Slade (1987), and was also in the Ca-exchanged form. Neither the Bingham nontronite nor the Phalaborwa vermiculite samples were given any further treatment.…”

Ion Exchanged Vermiculites with Lower Expansion Onset Temperatures

“…Several authors [9,29,30,46,47] also found that Palabora vermiculite has, comparatively, an unusually high level of iron. These iron ions (and also aluminium ions) are the main isomorphous substitutes for magnesium in the octahedral sites and also as considerable silica replacements in the tetrahedral sites [46].…”

“…These iron ions (and also aluminium ions) are the main isomorphous substitutes for magnesium in the octahedral sites and also as considerable silica replacements in the tetrahedral sites [46].…”